The present invention relates to a hydraulic torque wrench for tightening such fasteners as bolts and nuts.
A conventional hydraulic torque wrench comprises (a) a rotor driven for rotation, (b) an oil cylinder operatively connected to said rotor, (c) a main shaft installed for relative rotation in said oil cylinder, (d) two blades disposed about 180 degrees out of phase from each other circumferentially of said main shaft and retractably urged radially outwardly of said main shaft, (e) main shaft seal surfaces formed on the outer peripheral surface of said main shaft and circumferentially disposed about 90 degrees out of phase from said blades, (f) first seal surfaces formed on the inner peripheral surface of said oil cylinder so that they oil-tightly contact only said main shaft seal surfaces in a particular phase, (g) second seal surfaces formed on the inner peripheral surface of said oil cylinder so that they oil-tightly contact the projecting ends of said blades in said particular phase, wherein in said particular phase, one side of each of said blades defines a high pressure chamber while the other side defines a low pressure chamber.
In this type of hydraulic torque wrench, high and low pressure chambers are defined for every 180 degrees per revolution of the oil cylinder, so that percussion torque is produced twice per revolution of the oil cylinder. FIGS. 10a and 10b are cross-sectional views for explaining how percussion torque is produced in such torque wrench. As shown in FIG. 10a, two blades 102 are disposed about 180 degrees out of phase from each other circumferentially of a main shaft 101 and retractably urged radially outwardly of the main shaft 101. Seal surfaces 101a are formed at positions deviated some degrees toward one blade 102 (the lower blade 102 in the figure) from an axis a perpendicularly intersecting a line connecting blade receiving grooves S which receive the blades 102. The seal surfaces 101a slightly project radially outward from the outer peripheral surface of the main shaft 101.
On the other hand, the oil cylinder 103 has a cylinder chamber of cocoon-shaped cross section. The inner surface of the oil cylinder 103 has two second seal surfaces 103b formed thereon at diametrically opposite positions on its major axis. At diametrically opposite positions on its minor axis it is formed with two first seal surfaces 103a. The second seal surfaces 103b are adapted to contact the front surfaces of the blades 102, while the first seal surfaces 103a are adapted to contact the main shaft seal surfaces 101a. The first seal surfaces 103a are deviated some degrees from the direction of said minor axis in the same relationship as between the blades 102 and the main shaft seal surfaces 101a.
Thus, as shown in FIG. 10a, in a first particular phase condition in which the second seal surfaces 103b are contacted by the blades 102 and the first seal surface 103a are contacted by the main shaft seal surfaces 101a, high pressure chambers H and low pressure chambers L are alternately defined circumferentially of the main shaft 101. In a second particular phase condition established when the oil cylinder 103 has rotated through 180 degrees relative to the main shaft 101 from said first particular phase condition, as shown in FIG. 10b, the second seal surfaces 103b are contacted by the blades 102, but the first seal surfaces 103a and the main shaft seal surfaces 101a do not contact each other, creating a clearance therebetween. Therefore, there is no pressure difference produced and hence said high and low pressure chambers are not defined. In other conditions than these first and second particular phase conditions, no pressure difference is produced; high and low pressure chambers are defined in the first particular phase condition only. That is, percussion torque is produced once per revolution of the oil cylinder 103 relative to the main shaft.
In this conventional example, the arrangement must be such that the main shaft seal surfaces 101a and the first seal surfaces 103a are switched between contact and noncontact conditions by a slight clearance therebetween attending on 180-degree relative rotation and such that in the noncontact condition, communication clearances are defined between the main shaft seal surfaces 101a and the inner peripheral surface of the oil cylinder 103 and between the first seal surfaces 103a and the outer peripheral surface of the main shaft 101. Therefore, the processing of the main shaft seal surfaces 101a and the first seal surfaces 103a requires high precision, which, in turn, requires much time and labor in processing, leading to high cost.